Conventionally, in axial flow fans, tip seals of a labyrinth type have been used to reduce tip air leakage or the flow of air in a gap (on the order of 5 mm) between the shroud and rotor (fan) in an engine cooling fan assembly. Ribs have also been used in an effort to reduce this air leakage. A disadvantage of the labyrinth seal is that this seal is difficult to manufacture and that often the manufacturing tolerances limit the proper design of the seal. Ribs in the tip region only prevent the swirling component of flow from causing turbulence by reentering the fan. However, the ribs do not seal air leakage through the tip gap effectively.
Accordingly, there is a need to provide a labyrinth seal in a fan-shroud structure to decrease the gap between the rotor and shroud and to remove the swirling components of flow in the tip region of a fan so as to reduce noise with marginal losses in static efficiency.